A major goal of any dielectric deposition system is good step coverage. Step coverage refers to the ability of subsequent layers to evenly cover layers (“steps”) already present on the substrate. Facet etches are frequently used to provide superior step coverage. The standard facet etch uses a high energy argon ion which physically bombards the material being etched and thereby etches the oxide at an angle to allow subsequent material to have the best step coverage possible. However, if the argon ions etch through the oxide and reach metal or another conductor, they disperse their energy into the metal line or other conductor. This energy finds its way to a ground through a weak spot in the gate oxide thereby resulting in a blown gate.
In sputter etching, ions which impinge on horizontal surfaces have a minimal effect on etch rate and profile. However, the sputter yield of the etch at the corners is approximately four times that of the etch rate of a horizontal surface, thereby creating an extreme etch profile. The effect is the wearing away of the corners of a feature at approximately 45 degree angles. The material removed by the sputter etch is redeposited along the sides of the feature and along the surface of the substrate.
An issue associated with sputter etching is that some of the sputtered material redeposits frequently on the inside surfaces of the etching chamber. This redeposited material must be removed at intervals, thereby taking the etching chamber off-line.